Disney can lower the turnstile count, raise the prices of admission, and not lose a penny.
They would, however, lose Walt's original goal of a theme park accessible to the average middle class vacationer. Disney already gets some grief for being more expensive than the other Orlando parks; if they kicked up one-day admission to $300 (as someone else suggested), it'd be a PR nightmare.
As many have pointed out, when you buy a 7-10 day ticket, you are driving your daily cost way down below $50 per day.
When we last went to SeaWorld, with the second day free deal it cost about $30/day. Right now it's $41/day, and that's without discounts. It's much easier to find serious discounts for SeaWorld or Universal; very tough to find discounts for Disney beyond 10%.
The Flex Ticket (which gets you 14 consecutive days in the Universal parks, SeaWorld, Aquatica, or Wet and Wild) costs $23/day. Going on your numbers for WDW, Disney's charging almost twice the going rate.
Most inferior amusement parks cost that much if not more.
Few people go to those inferior amusement parks for more than one day. And few of those amusement parks are making the dedicated restaurant and hotel money Disney rakes in, let along all the other shopping the average Disney-goer does. Disney's parks function to bring people in and keep them inside the Disney Bubble, where everything costs boatloads more than outside but people pay it anyhow. Comparing WDW's parks to amusement parks is comparing two very different things, with two entirely different money-making methods.
Greens fees for 18 holes at a resort golf course are north of $150. .
Only if you're going to Torrey Pines or someplace like that. Or Disney, apparently.

But even at places like Torrey Pines you can get a considerable discount by getting a Twilight reservation, which will take it down to much less than $100. And the average golfer isn't paying that much; golf resorts like World Golf Village in St. Augustine charge more like $70, while Fairfield Glade and a lot of the Cumberland resorts it's easy to get below $50.
And, as you yourself point out, Disney charges more for golf than it does for the theme parks. Two different things, with very different clientele. A golfer is paying for himself; a parent taking their family to a theme park is paying for self and everyone else.
Many people have repeated here that "Disney is a bargain". And it is. But it shouldn't be. The leader of the industry that produces the best product shouldn't be a "bargain".
Why not? Historically, that has often been the case. The best is often produced by the most efficient, who can produce the most for the least, and they often accomplish that by serving the most customers. The more customers, the lower the price of serving each customer. Disney is making ridiculous profits serving cafeteria food at gourmet restaurant prices, and renting out tiny hotel rooms for more than some 4 star hotels, so why should they change? They are selling the experience, and plenty of people are happy paying for same.
Raise admission fees 15%-20% during those heavy times and try to control crowds that way.
Rumor is they're thinking about doing something like that (tiering
ticket prices as they have tiered hotel prices), which I think is a great idea.
90% of the complaints I am hearing are related to crowds, and far fewer relate to money.
I've heard more complaints about money than crowds, myself. There are still plenty of people who think WDW is overpriced. And, compared to the other Orlando theme parks, it is! WDW isn't competing with Six Flags of Anywhere -- it's competing with Sea World Orlando, Universal Orlando, and all the stuff along North International Drive. And, even at the lowest alternatives, it's charging twice as much as any of them. In terms of first-day admittance, they're a lot closer, but Universal's second day cost $40 less than Disney's, their three day ticket is $100 less, and so on.
People who spend a lot of time golfing and skiing may not be money sensitive when it comes to WDW tickets, but I bet Disney's base clientele is.